Precipitation behavior of α2 phase and its influence on mechanical properties of binary Ti-8Al alloy

Abstract The precipitation behavior of Ti3Al (α2) and its effect on the tensile properties and fracture toughness of the binary Ti-8Al alloy were investigated. Ti-8Al alloy was firstly solution-treated to obtain Widmanstatten structure and then aged for different aging times to promote α2 precipitation. Transmission electron microscopy and atom probe tomography analyses were employed to characterize the presence of α2 phase. The results showed that the size and volume fraction of α2 precipitates increased as aging time prolonged. The relationship between the mechanical properties and α2 precipitates was evaluated. The increase in the volume fraction of α2 enhanced the alloy strength, meanwhile, induced the long-rang planar slipping and inhibited the twinning activity. This could intensify strain localization and decrease fatigue crack tip plastic zone size (CTPZ), leading to the reduction of ductility and fracture toughness. The in-situ tensile test results revealed that the activation of slipping and colony rotations both occurred in response to deformation. Also, it was found that the increase of the plastic strain enhanced the intensity of strain localization, and the misorientation across the shearing band in the large α colony enhanced the stress concentration area which would promote the crack nucleation. In light of these findings, the tailoring of α2 precipitation in titanium alloys are required in the design of high-performance alloys for structural applications.